Lensfree imaging has been recently gaining more emphasis to create modalities that can potentially eliminate bulky optical components to perform microscopy on a chip. Such on-chip microscope designs would especially benefit microfluidic systems to create powerful capabilities especially for medical diagnostics and cytometry applications. Being light-weight and compact, lensfree imaging can also potentially create an important alternative to conventional lens-based microscopy especially for telemedicine applications.
Metallic apertures support surface plasmon waves that are localized to the near-field of the aperture structure. Physical properties of these plasmonic waves, by their nature, are rather sensitive to the local refractive index of the medium surrounding the aperture region. As the size of the metallic aperture goes sub-wavelength, direct transmission of light through the aperture becomes extremely inefficient and the transmission behavior of these apertures starts to be dominated by plasmonic effects, exhibiting strong sensitivity to the refractive index of the surrounding medium as well as to the wavelength, polarization, and the angle of the illumination light. Surface plasmon resonance using metal films has been used, for example, gas detection and biosensing applications. While metallic films and apertures have been used in some sensing applications, these have not been integrated into a lensfree system that avoids the need for lenses, mechanical scanning or other bulky optical/mechanical components.